1. Field of the Invention
The present invention relates to a charger calibrating device, in particular to a digital flash lamp charger calibrating device and a calibrating method thereof with a lower cost and a higher efficiency.
2. Description of the Related Art
In digitals camera and digital camcorders, a flash lamp module is a necessary component, and a flash lamp circuit requires a charging capacitor to store energy in order to trigger an inert gas inside a lamp tube of a flash lamp to emit light. Such capacitor generally has a charging voltage up to 300 volts. To achieve a high voltage of over 300 volts for the capacitor voltage, the flash lamp circuit generally comes with a charging circuit to convert and supply the electric energy of a battery into the capacitor.
During the production process of a camera, a maximum flash lamp charging time is set to comply with a specific technical specification for all produced cameras, such that each camera has substantially the same charging time under the condition of the same voltage. In general, a flyback converter is usually used as the charging circuit of a camera.
With reference to FIG. 1 for a schematic circuit diagram of a charging circuit of a conventional flash lamp charger, the flyback converter 1 controls the ON/OFF of an n-type metal oxide semiconductor Q1 by a pulse width modulation (PWM) circuit P1 and charges a capacitor by an inductor in the circuit. If the PWM circuit P1 is situated in a high level period, a gate of the semiconductor Q1 is situated at a high level and an ON state for charging the inductor of a primary side np of a transformer T1.
On the contrary, it is an OFF sate if the gate of the semiconductor Q1 is situated at a low level. At the same time, a secondary side ns of the transformer T1 will induce a current, and the current flows through a diode D1 to charge a capacitor C1, and the inductance of the primary side np of the transformer will convert and transfer the energy stored at the gate of the semiconductor Q1 during in the high level period to the capacitor C1. Therefore, the voltage of the capacitor C1 can be charged to a level over 300 volts by continuous switching the semiconductor Q1.
However, hardware components have errors, such as the inductance of the primary side np may have an error of +/−20%. Since the semiconductor Q1 is situated at the ON state, the current passing through the primary side np will increase with time. The smaller the inductance, the faster is the rising current. On the contrary, the larger the inductance, the slower is the rising current. Therefore, the error of the inductance will affect the charging time of the flyback converter. To avoid the aforementioned situation, related manufacturers generally install a resistor R3 in the flyback converter, that monitoring and control the current passing through the primary side np by a comparator CP1. When the current rises to a certain level, the resistor R3 will have a voltage value greater than threshold voltage value (Vth). Now, the PWM circuit P1 turns off the semiconductor Q1 and terminates the continual charging of the inductor of the primary side np to control the charging time of the capacitor C1.
This method requires additional resistor R3 and comparator CP1 installed in the circuit and incurs a higher cost. In addition, the resistor R3 will generate heat and lower the efficiency of the charger. Therefore, it is a main subject for the present invention to design a flash lamp charger calibrating device capable of lowering the manufacturing cost of the flash lamp charger, improving the charging efficiency, and enhancing the production capacity and yield rate of camera or camcorder products.